Planet definitions and the Creator

The downgrading of Pluto causes controversy

10 November 2006

Scientists have recently been asking the question,
‘What is Pluto?’ In a controversial decision on 24
August 2006, the International
Astronomical Union (IAU) voted to accept
a new definition of the term ‘planet’. The IAU is
an internationally recognized organization that is responsible for
naming objects in space. The definition reduces the number of planets
in our solar system to eight, excluding Pluto and certain other
objects. The astronomical community has had varied reactions to this
decision. Why is there so much controversy over this decision and why
have astronomers stopped considering Pluto a planet? Ultimately the
question of how to define a planet arises because it is challenging for
man to categorize some of the objects God created.

Planetary scientists have debated for years whether
Pluto should be considered a planet. Pluto is very different from the
other eight
objects called planets. It is much smaller, has a tilted orbit and a
different composition from the large gaseous planets in the outer
solar system. For some years it has been known that Pluto possessed a
moon called Charon, then recently two additional small objects were
discovered orbiting Pluto.1
These new moons have not
yet been named.

Other objects have been discovered orbiting our Sun
that are even more
distant than Pluto. The region beyond the planet Neptune is often
called the Kuiper Belt or the trans-Neptunian region. There also are a
few other small bodies in the solar system in various regions that defy
traditional categories like planet, moon, asteroid, and comet.
Scientists have sometimes struggled with what to call them. One object
beyond Pluto’s orbit had the official designation of 2003
UB313 (now called Eris).2
It is even larger than Pluto. If Pluto is a planet, should we consider
Eris a planet also? Another similar object exists beyond Pluto that
seems to be a little over half Pluto’s size. It is called
Quaoar.3
There are more and more objects being discovered in the Kuiper Belt
region. Ceres is the largest of the asteroids in the region between Mars
and Jupiter, 940 km (590 miles) in diameter. When Ceres was first
discovered it was considered a planet, but then as other small objects
were found between Mars and Jupiter Ceres was reclassified as an
asteroid.

After
NASA

On
16 August the IAU proposed a
new definition of planet that would
have increased the number of planets from nine to twelve. By that
definition, Charon, Eris, and Ceres would all have been reclassified as
planets. Also by this definition it is likely there would have been
many more objects added to the list of planets in the future as
astronomers continued to discover new objects beyond Pluto. However,
the 12 planet definition was not adopted. Rather, a definition was
adopted that no longer considers Pluto to be a planet, nor Charon,
Ceres, or UB313. It establishes three main categories to encompass the
various objects in our solar system.4
The categories are Planet, Dwarf Planet, and Small Solar System Bodies.
The definition of Dwarf Planet is based on the definition of
Planet. Small objects that are neither Planets nor Dwarf Planets (such
as comets) will be referred to as Small Solar System Bodies (which
replaces the old term ‘Minor Planet’). These would
include asteroids, comets, and Near Earth Objects.

For an object to be considered a planet, it must
pass certain tests, by
the 24 August IAU definition. First, it must orbit a star (not orbit a
planet) and it cannot be a star. The second test has to do with its
size and shape. It must have enough matter (or mass) so that its own
gravity would pull it into a spherical shape. Note that scientists tend
to assume natural forces alone are all that was involved in forming
planets. It may be that gravity could pull an object into a spherical
shape, or it could be that God created the object supernaturally, using
a spherical shape to make the body stable. Gravity does tend to make
large bodies round. When an object’s inward force of gravity
balances
with other interior forces to make it spherical in shape, it is said to
be in hydrostatic equilibrium. It is believed this requires a rocky
object to be about 800 km (500 miles) in diameter. If a body is not in
hydrostatic equilibrium, then it will change in some way until forces
get back in balance.

Scientists know about gravity and about how the
properties of rock,
ice, and other materials in a body can determine how rigid it is and
what shape it is. But no one has observed gravity pulling a large mass
into a planet-sized sphere. Actually in evolutionary planet origin
models, it is believed that something had to melt the object before
gravity could pull it into a sphere with layers in its interior. So,
there is more to the problem than just gravity. Also, we do not know
that planets have always been or will always be in hydrostatic
equilibrium. Events in the past such as large impacts or geologic events
could have put an object out of equilibrium. So, it may be difficult to
apply the second test, at least for some cases.

It seems unclear whether even Earth, Jupiter, or
Neptune would pass
this [test to be called a planet].

Pluto would meet both
of the above planet tests, being about 2,300 km
(1,500 miles) in diameter, but Pluto does not pass the third test of a
planet. A planet, by the new definition, must have cleared other
objects away from near its own orbit. This last test assumes that an
object large enough to pull together by gravity would over time cause
small objects near it to fall into the planet or be pulled away into
some other part of the solar system. Because the orbits of Pluto and
Neptune come very close to each other, Pluto does not meet this
requirement. And even though their orbits are so close, their motions
are so timed that Pluto and Neptune can never collide.5 For every two
complete orbits
made by Pluto, Neptune makes exactly three orbits. The origin of this
resonant motion is still a mystery to planetary scientists.

The third test has been criticized by a number of
astronomers. It seems
unclear whether even Earth, Jupiter, or Neptune would pass the third
test of a planet. For example, there are a number of objects known as
Near Earth Objects (NEOs) close to Earth’s orbit.

Objects that pass the first two tests but not the
third one will now be
known as Dwarf Planets. Dwarf Planets by this definition could be
anywhere in the solar system, and include Ceres, Eris, and Pluto.

This test of clearing the orbit also relates to the
question of the age
of the solar system. By assuming it is 4.5 billion years old,
evolutionist astronomers have given themselves plenty of time for small
objects to be cleared away from orbits. On the other hand, there are
processes that could actually add small objects
to planet orbits in some cases. There are also cases where asteroids or
moons are in special stable positions, sharing an orbit with another
object. There are asteroids like this (called the Trojans) that share
Jupiter’s orbit. They will never be ‘cleared
out’
because of their special stable positions.

There is also a small list of NEOs that are known as
Earth’s
co-orbitals; one of them is named Cruithne.6
Cruithne follows a very complex path that makes it roughly oscillate
around Earth’s orbit. Cruithne’s orbit has been
variously described as
a corkscrew or horseshoe. These objects roughly share Earth’s
orbit,
but they are not bound to Earth like the Moon and they don’t
follow
Earth’s orbit either; instead, they have a complicated motion
around
Earth’s orbit. The motion of these coorbitals is so unusual
that they
do not even follow Kepler’s Laws of planetary motion! This
makes them
different from all other known objects in the solar system. Yet, they
seem to be stable in their complex ‘dance’.

The God of the Bible is a Creator who makes both the
large and the
small for his purposes. In recent years we have learned much about the
Small Solar System Bodies, as the new definition calls them.

Christians should bear in mind that scientific observations of
planets today do not tell scientists how the planets formed. The Bible
puts the origin of stars, planets, moons, galaxies, and all other
objects in space all on the fourth day of the Creation Week. This
clearly requires supernatural creation. In the theories accepted by
most scientists today, the origins of planets and some other objects in
space were separated by billions of years.

Whether Pluto is considered a planet or not by
planetary scientists,
there is great interest in exploring it. In January 2006 NASA launched
a spacecraft known as New Horizons that will travel all the way to
Pluto, arriving in the year 2015 if all goes well. If the August 24 IAU
definition remains in effect, the number of planets will likely remain
at eight. But eventually there may be many objects in the Dwarf Planet
category, as our knowledge of Kuiper Belt Objects and asteroids
increases. The Creator’s work still surprises scientists and
new
discoveries create a need for new categories.

Computer simulations
of the motion
of Pluto and Neptune show that Pluto and Neptune would be stable in
their current orbits and never collide for at least several tens of
thousands of years. Stern, A.and Mitton, J., Pluto and Charon,
John Wiley & Sons, New York, USA, pp. 139–143, 1998. Return to text

This semi-technical
site is from one
of the discoverers of Cruithne. It has some graphics showing the
complexities of Cruithne’s motion around Earth’s
orbit. Wiegert, P., et
al, Near-Earth asteroid 3753
Cruithne—Earth’s
curious campanion,
13 September
2006. Return to text

Wayne
Spencer,
B.S., M.S. obtained his master’s degree in physics from
Wichita State University in Kansas. Active in creationist circles, he
has taught science and maths, and now works in computer technical
support.
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